1. Field of the Invention
This invention relates generally to a system and method for determining when to replace a compressor air filter in a fuel cell system and, more particularly, to a system and method for determining when to replace a compressor air filter in a fuel cell system that uses a compressor map to determine compressor inlet pressure based on the airflow through the compressor and the compressor discharge pressure.
2. Discussion of the Related Art
Hydrogen is a very attractive fuel because it is clean and can be used to efficiently produce electricity in a fuel cell. A hydrogen fuel cell is an electro-chemical device that includes an anode and a cathode with an electrolyte therebetween. The anode receives hydrogen gas and the cathode receives oxygen or air. The hydrogen gas is dissociated in the anode to generate free protons and electrons. The protons pass through the electrolyte to the cathode. The protons react with the oxygen and the electrons in the cathode to generate water. The electrons from the anode cannot pass through the electrolyte, and thus are directed through a load to perform work before being sent to the cathode.
Proton exchange membrane fuel cells (PEMFC) are a popular fuel cell for vehicles. The PEMFC generally includes a solid polymer electrolyte proton conducting membrane, such as a perfluorosulfonic acid membrane. The anode and cathode typically include finely divided catalytic particles, usually platinum (Pt), supported on carbon particles and mixed with an ionomer. The catalytic mixture is deposited on opposing sides of the membrane. The combination of the anode catalytic mixture, the cathode catalytic mixture and the membrane define a membrane electrode assembly (MEA). MEAs are relatively expensive to manufacture and require certain conditions for effective operation.
Several fuel cells are typically combined in a fuel cell stack to generate the desired power. For example, a typical fuel cell stack for a vehicle may have two hundred or more stacked fuel cells. The fuel cell stack receives a cathode input reactant gas, typically a flow of air forced through the stack by a compressor. Not all of the oxygen is consumed by the stack and some of the air is output as a cathode exhaust gas that may include water as a stack by-product. The fuel cell stack also receives an anode hydrogen reactant gas that flows into the anode side of the stack. The stack also includes flow channels through which a cooling fluid flows.
The fuel cell stack includes a series of bipolar plates positioned between the several MEAs in the stack, where the bipolar plates and the MEAs are positioned between two end plates. The bipolar plates include an anode side and a cathode side for adjacent fuel cells in the stack. Anode gas flow channels are provided on the anode side of the bipolar plates that allow the anode reactant gas to flow to the respective MEA. Cathode gas flow channels are provided on the cathode side of the bipolar plates that allow the cathode reactant gas to flow to the respective MEA. One end plate includes anode gas flow channels, and the other end plate includes cathode gas flow channels. The bipolar plates and end plates are made of a conductive material, such as stainless steel or a conductive composite. The end plates conduct the electricity generated by the fuel cells out of the stack. The bipolar plates also include flow channels through which a cooling fluid flows.
Fuel cell systems typically employ an air filter at the inlet to the cathode compressor to remove contaminants and particulates that would otherwise degrade compressor and fuel cell stack performance. Air filters for fuel cell systems are typically more complex than a typical internal combustion engine air filter, often filtering to HEPA standards of 0.3μ as opposed to 10-15μ for an internal combustion engine air filter. Fuel cell system air filters also typically absorbing various chemicals, such as acid gases and hydrocarbons. Almost all compressors employed as the cathode oxygen provider would be sensitive to inlet flow restrictions caused by a restricted filter, especially a turbo-compressor. If the air filter is restricted, the inlet to the compressor becomes depressed, which limits the fuel cell system's maximum power while consuming additional energy, further reducing performance. Further, for a turbo-compressor, if the air filter fails as a result of being torn or otherwise mispositioned as a result of the force of the compressor air pulling on the air filter, dust and other contaminants that may enter the compressor may damage the compressor and its air bearings.
Currently, without a dedicated compressor inlet pressure sensor, no technique or process is used in the art for detecting when the air filter in the fuel cell system should be replaced, which otherwise might cause compressor failure.